The present invention relates to pulse wave detecting devices and, more particularly, to a pulse wave detecting device for detecting a pulse wave by transmitting and receiving an ultrasonic wave to and from an artery.
It is broadly implemented to detect a pulse wave from blood flow through an artery, at medical sites or in health care. Pulse wave detection is broadly conducted by electronically, automatically detecting a pulse frequency or the like by using a pulse wave detecting device, besides detecting of a pulse frequency per a given time through palpation.
The devices which electronically detect a pulse wave and acquire a pulse frequency include those having a piezo-type piezoelectric element that is to be positioned as a sensor over an artery in order to detect a pulse frequency from a pressure change of a surface skin caused due to an artery pressure change (surface skin displacement by pressure) and those using an ultrasonic wave to detect a pulse frequency.
The pulse wave detecting devices using an ultrasonic wave include those utilizing the Doppler effect due to blood flow, as proposed, e.g. in Japanese Patent Laid-open No. 214335/1989 and U.S. Pat. No. 4,086,916.
With reference to FIGS. 5A and 5B, the conventional pulse wave detecting device 1 will be explained on its basic structure and operation.
The pulse wave detecting device 1 is mounted on a wrist watch and used as below.
First, a pulse wave probe having an ultrasonic wave transmitting transducer 11 and ultrasonic wave receiving transducer 21 formed by a plurality of piezoelectric vibrators is slidably mounted by screwing in an optimal position of a watch strap for detecting a pulse wave (e.g. in a position where the pulse wave detection signal assumes a maximum).
When actually detecting a pulse wave by the pulse wave detecting device 1, as shown in FIGS. 5A and 5B an ultrasonic wave A is transmitted from the piezoelectric element of the ultrasonic wave transmitting transducer 11 driven by a drive part 12 toward an artery 2 in a human body surface 3. Then, a reflection wave B reflected by the blood flowing through the artery 2 is received by the ultrasonic wave receiving transducer 21.
Next, the reflection ultrasonic wave B thus received is waveform-detected by a receiving part 22. The waveform-detected ultrasonic wave is processed in a signal processing part 23 to detect a change in frequency or phase of the reflection wave B. The signal processed by the signal processing part 23 is displayed of its waveform on a display device of an output part 24.
When the heart contracts, the blood flowing through the artery 2 is high in speed. Accordingly, the reflection wave of ultrasonic wave transmitted toward the artery 2 is increased in frequency due to the Doppler effect. Conversely, when the heart expands the blood flowing speed is low and hence the frequency thereof decreases.
In this manner, an ultrasonic wave is radiated to a blood flow in an artery varying in speed depending on heart pulsation. By detecting a change of frequency, it is possible to detect a pulse wave, and furthermore a pulse frequency or a blood flow speed.
However, the above pulse wave detecting device 1 has the following defects.
First, when wearing the wrist watch type pulse wave detecting device 1 on a wrist, it takes time in adjusting and positioning, by sliding, the pulse wave probe to an optimal position for detecting a pulse wave.
Second, even where the wrist watch type pulse wave detecting device 1 be worn at an optimal position on the wrist, if the pulse wave probe is deviated in position because of a subsequent movement of the body or the like, then correct measurement would be impossible to conduct.
It is therefore a first object of the present invention to provide a pulse wave detecting device which is capable of automatically positioning a pulse wave probe in an optimal position when putting the pulse wave detecting device.
It is a second object of the invention to provide a pulse wave detecting device in which a pulse wave probe can be newly positioned automatically in an optimal position even when there is positional deviation in the pulse wave probe after wearing the pulse wave detecting device.
In the present invention, the first and second objects are achieved by a pulse wave detecting device comprising transmitting means having a plurality of transmitting piezoelectric vibrators to transmit an ultrasonic wave toward an artery, receiving means having a plurality of receiving piezoelectric vibrators to receive an ultrasonic wave propagating through the artery, pulse wave information acquiring means for acquiring pulse wave information from an ultrasonic wave signal transmitted from any one of the transmitting piezoelectric vibrators and received by any one of the receiving piezoelectric vibrators, signal intensity detecting means for detecting a signal intensity of the received ultrasonic wave by the receiving means, and optimal combination determining means for determining an optimal combination of a transmitting piezoelectric vibrator to be used by the transmitting means and a receiving piezoelectric vibrator to be used by the receiving means on the basis of the signal intensity of the ultrasonic wave detected by the signal intensity detecting means, and causing the transmitting piezoelectric vibrator of the optimal combination to transmit an ultrasonic wave and the receiving piezoelectric vibrator of the optimal combination to receive the ultrasonic wave.
Also, the optimal combination determining means has switching means to switch to any one of the transmitting piezoelectric vibrators and selecting means to select any one of the receiving piezoelectric vibrators, the optimal combination determining means causing the switching means and the selecting means to change in order over the transmitting piezoelectric vibrators and the receiving piezoelectric vibrators, respectively, and determining an optimal combination of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator assuming a maximum value in signal intensity of an ultrasonic wave.
Also, the optimal combination determining means causes the switching means and the selecting means to periodically change in order over the transmitting piezoelectric vibrators and the receiving piezoelectric vibrators, respectively, and determines an optimal combination of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator assuming a maximum value in signal intensity of an ultrasonic wave.
Also, the optimal combination determining means, when a signal intensity of an ultrasonic wave detected by the signal intensity detecting means decreases, causes the switching means and the selecting means to change in order over the transmitting piezoelectric vibrators and the receiving piezoelectric vibrators, respectively, and determines an optimal combination of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator assuming a maximum value in signal intensity of a ultrasonic wave.